docs: def save(self, filename):
          """
          Store AEAD in a file.
  
          @param filename: File to create/overwrite
          @type filename: string
          """
          aead_f = open(filename, "wb")
          fmt = "< B I %is %is" % (pyhsm.defines.YSM_AEAD_NONCE_SIZE, len(self.data))
          version = 1
          packed = struct.pack(fmt, version, self.key_handle, self.nonce, self.data)
          aead_f.write(YHSM_AEAD_File_Marker + packed)
          aead_f.close()